The present invention relates in general to impact tools such as hammers, axes, hatchets and similar hand tools and is concerned more particularly with a method for forming an improved connection between the tool head and handle which reduces the tendency in such tools under normal conditions of usage to develop looseness between and separation of the head and handle. The invention is particularly advantageous for use in the manufacture of such tools where the handle is formed of non-metallic material such as wood or plastic.
Impact tools such as hammers have long been made with metallic heads and non-metallic handles, with the end of the handle inserted into and secured to a central opening or eye in the head. The principal and traditional way of forming the connection between the head and end of the handle has been to provide the eye of the head with an outward flare or enlarged cross-section toward its exit end and to expand the end of the handle which has been inserted through the smaller entrance end of the eye into tight contact throughout with the eye by wedging. This is accomplished by driving one or more wedges into the exposed end of the hammer forcing the end of the handle to expand or enlarge and bringing its periphery into compressive contact with the eye. While such connections are initially very tight, it is well known that they tend to deteriorate rapidly during normal usage of the tool. The exceedingly large and intermittent stresses that occur during usage of the tool together with such other factors as the presence of fissures in the end of the handle produced by the wedges, and the alternate swelling and contraction of the handle end as a result of changing ambient humidity conditions, all contribute to rapid deterioration of the tight fit resulting in looseness and eventual separation.
With the advent of improved adhesives and particularly the strong resin adhesives such as epoxy resins, such materials have been used to bond the handle to the eye of the tool head without or in combination with wedging. In the usual process employed, the adhesive is poured into the exit end of the eye after the handle is inserted and the tool is then permitted to stand until the adhesive sets which usually takes a substantial period of time and which is usually accompanied by shrinkage of the adhesive. Moreover, it has been found that in order to produce an effective connection including damping of the vibrations of the tool head, it is necessary when employing this technique to provide direct contact between the handle and metallic head throughout a substantial portion of the eye thus greatly reducing the available area for adhesive bonding. These limitations together with the inherent limitations of the bonding material frequently results in rapid fracture or release of the adhesive bond under stress, thus permitting the handle to loosen and be released without material increase in service life. Attempts to use rubber and rubber-like fillers or packings have met with similar difficulties.
Accordingly, it is an object of the present invention to provide a method for forming a handle connection for impact tools which avoids the above-mentioned disadvantages and which affords a tight effective connection between the head and handle having a long service life before repair or replacement is required.
Another object is to provide such a method which can be carried out without difficulty using readily available materials and with consistent high quality whereby the use of the invention is economically attractive as well as producing improved results.
An additional object is to provide a economical method of forming a handle connection requiring a minimum of manual operations and requiring a minimum of operating time.
A further object is to form a handle connection in a manner which will not adversely affect the desired qualities of the tool such as balance and absorption of vibrations and which will produce a connection that will not deteriorate due to external or ambient conditions.
Other objects will be in part obvious and in part pointed out in more detail hereinafter.
These and related objects are accomplished in accordance with the present invention by forming the eye of the tool head and the end of the handle with cooperating contours including spaced apart opposed surfaces in a direction axially of the handle and preferably at least one inclined camming or wedging surface on the interior of the eye and a peripheral recess in its handle, injecting a molding thermoplastic resin into the space between the surfaces under sufficient pressure to compress the end of the handle, the thermoplastic being heated to a flowable condition, and maintaining said pressure while permitting the thermoplastic to solidify, whereby the thermoplastic forms a tough, hard and rigid mechanical interlock compressibly engaging the handle and in intimate contact with the head thus forming a tight and durable connection effective over long periods of service.
A better understanding of the invention will be obtained from the following detailed description and accompanying drawing illustrating various preferred embodiments in which the principle of the invention is employed.